U.S. patent application number 11/747089 was filed with the patent office on 2008-11-13 for turbocharger shaft over-speed compensation.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Michiel J. Van Nieuwstadt, Yong Shu.
Application Number | 20080276614 11/747089 |
Document ID | / |
Family ID | 39537272 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080276614 |
Kind Code |
A1 |
Shu; Yong ; et al. |
November 13, 2008 |
Turbocharger Shaft Over-Speed Compensation
Abstract
A method for controlling engine operation, the engine having a
turbocharger coupled between an intake and exhaust manifold of the
engine via a turbocharger shaft, the method comprising dynamically
determining turbocharger shaft speed based at least on intake and
exhaust manifold conditions using a torque balance across the
turbocharger; and adjusting turbocharger boosting to adjust
turbocharger shaft speed in response to said dynamically determined
turbocharger shaft speed.
Inventors: |
Shu; Yong; (Northville,
MI) ; Nieuwstadt; Michiel J. Van; (Ann Arbor,
MI) |
Correspondence
Address: |
ALLEMAN HALL MCCOY RUSSELL & TUTTLE, LLP
806 S.W. BROADWAY, SUITE 600
PORTLAND
OR
97205
US
|
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
39537272 |
Appl. No.: |
11/747089 |
Filed: |
May 10, 2007 |
Current U.S.
Class: |
60/602 ;
60/611 |
Current CPC
Class: |
F02D 41/0007 20130101;
F02D 41/187 20130101; Y02T 10/12 20130101; F02D 2041/1416 20130101;
F02D 41/221 20130101; F02D 41/1448 20130101; F02B 39/16 20130101;
F02B 2039/168 20130101; F02D 2041/1417 20130101; Y02T 10/144
20130101; F02B 37/24 20130101; F02D 2200/703 20130101; F02D
2200/0406 20130101 |
Class at
Publication: |
60/602 ;
60/611 |
International
Class: |
F02D 23/00 20060101
F02D023/00; F02B 33/44 20060101 F02B033/44 |
Claims
1. A method for controlling engine operation, the engine having a
turbocharger coupled between an intake and exhaust manifold of the
engine via a turbocharger shaft, the method comprising: dynamically
determining turbocharger shaft speed based at least on intake and
exhaust manifold conditions using a torque balance across the
turbocharger; and adjusting turbocharger boosting to adjust
turbocharger shaft speed in response to said dynamically determined
turbocharger shaft speed.
2. The method of claim 1 wherein said adjusting limits turbocharger
shaft speed, even during transient turbocharger conditions, to be
below a threshold value.
3. The method of claim 2 wherein said adjusting includes adjusting
a turbocharger wastegate.
4. The method of claim 2 wherein said adjusting includes adjusting
a variable geometry turbocharger position.
5. The method of claim 2 further comprising dynamically determining
turbocharger shaft speed additionally using feedback based on
steady state turbocharger maps.
6. The method of claim 5 wherein said feedback includes
integration.
7. The method of claim 6 wherein said integration is adjusted based
on turbocharger operation.
8. The method of claim 7 wherein said dynamically determining is
based on turbocharger inertia, compressor airflow, turbine airflow,
and temperature.
9. A method for controlling engine operation, the engine having a
turbocharger coupled between an intake and exhaust manifold of the
engine via a turbocharger shaft, the method comprising: dynamically
estimating turbocharger shaft speed based on intake and exhaust
flow and turbocharger inertia using a torque balance across the
turbocharger, said dynamic estimate including feedback based on
steady state turbocharger mapping data, said feedback including an
integrated term; adjusting said integrated term based on a change
in steady state turbocharger operation using steady state mapping
data; and adjusting turbocharger boosting to limit turbocharger
shaft speed in response to said dynamically estimated turbocharger
shaft speed.
10. The method of claim 9 wherein said adjusting limits
turbocharger shaft speed, even during transient turbocharger
conditions, to be below a threshold value.
11. The method of claim 10 wherein said adjusting includes
adjusting a turbocharger wastegate.
12. The method of claim 10 wherein said adjusting includes
adjusting a variable geometry turbocharger position.
13. The method of claim 9 wherein said dynamically determining is
based on turbocharger inertia, compressor airflow, turbine airflow,
and temperature.
14. The method of claim 13 wherein the engine is a diesel
engine.
15. A system comprising: a diesel engine; a variable geometry
turbocharger having a turbocharger shaft coupled between an intake
and exhaust of the diesel engine; a controller for dynamically
determining turbocharger shaft speed based at least on intake and
exhaust manifold conditions using a torque balance across the
turbocharger and adjusting turbocharger boosting via vane position
to limit turbocharger shaft speed in response to said dynamically
determined turbocharger shaft speed, the controller accounting for
altitude effects on dynamic and steady state turbocharger
operation.
16. The system of claim 15 where the controller determines manifold
pressure, exhaust pressure, and atmospheric pressure to dynamically
determine turbocharger shaft speed.
17. The system of claim 16 where the controller further uses an
integral action to reduce steady state error.
18. The system of claim 17 where the controller further adjusts
engine operation during said limiting of shaft speed to reduce
engine output torque effects.
Description
BACKGROUND AND SUMMARY
[0001] Engines of motor vehicles may use turbochargers to achieve
various advantages in operation, such as increased torque, reduced
fuel economy, etc. However, turbochargers may have limited
operating regions.
[0002] Various approaches have been used for turbocharger boost
control, and limiting of excessive turbocharger shaft speeds. One
example is described in U.S. Pat. No. 6,539,714. In this example,
an estimate of the turbocharger rotational speed is determined as a
function of the compressor pressure ratio, the temperature signal
and the engine speed signal.
[0003] The inventors have recognized several issues with such
approaches, especially with regard to higher performance
turbochargers that may be used that operate at higher loads and
higher speeds. Further, using estimates based on prior approaches,
typically generates larger estimates during transient dynamic
conditions, thus resulting in a more conservative setting of
turbocharger operation to reduce transient over-speed operation. In
other words, due to issues of transient over-speed operation,
system typically limit boost levels below that actually. For
example, with regard to the example approach indicated above,
transient errors may be generated because only intake conditions
are considered, or because there is no dynamic compensation.
[0004] Thus, in order to address at least some of the above issues,
dynamic compensation for turbocharger over-speed shaft protection
may be used. In one specific example, the operation may include
intake and exhaust flow dynamics, as well as turbocharger dynamics.
In this way, more accurate, and dynamic, over-speed compensation
may be used to more accurately limit engine and/or boost operation
to limit shaft speed during dynamic turbocharger operation
[0005] As another example, an accurate estimate of turbocharger
shaft speed can be determined based on a dynamic observer which
uses a turbocharger torque balance as a dynamic term and a
turbocharger steady state map as a static term, thereby including
both the intake and exhaust side dynamics together with turbine
shaft speed dynamics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 shows a simplified schematic diagram of a diesel
engine system equipped with an exhaust gas recirculation system and
a variable geometry turbocharger.
[0007] FIG. 2 is a flow diagram for controlling engine and
turbocharger operation.
[0008] FIG. 3 is a flow diagram for using estimated shaft speed to
adjust vane position of the turbocharger.
[0009] FIG. 4 is a graph depicting a prophetic example of how turbo
speed can vary with time.
DETAILED DESCRIPTION
[0010] FIG. 1 shows a simplified schematic diagram of a diesel
engine system 10 equipped with an exhaust gas recirculation (EGR)
system 12 and a variable geometry turbocharger (VGT) 14. The
turbocharger may be a high performance turbocharger designed to
operate at higher speeds and loads for sustained durations or at
sustained temperatures, for example. While this example shows a
variable geometry turbocharger, a turbocharger having an adjustable
wastegate 90 in bypass 92 around the turbine side may also be used
as indicated in FIG. 1. Also, a bypass 94 may be provided around
the compressor side, having an adjustable valve 96 located
therein.
[0011] A representative engine block 16 is shown having four
combustion chambers 18, although more or fewer cylinders may be
used if desired. Each of the combustion chambers 18 includes a
direct-injection fuel injector 20. The duty cycle of the fuel
injectors 20 may be determined by the engine control unit (ECU) 24
and transmitted along signal line 22. For example, a common rail
direct injection system may be used.
[0012] Air enters the combustion chambers 18 through the intake
manifold 26, and combustion gases are exhausted through the exhaust
manifold 28 in the direction of arrow 30.
[0013] In the depicted embodiment, the intake valves and exhaust
valves (not shown) may be actuated by a fixed cam or by variable
cam timing (VCT) 91 via signal line 93. In some examples, variable
valve lift (VVL), cam profile switch (CPS), among other valve
control systems may be used to adjust operation of one or more of
the intake and/or exhaust valves. Alternatively, electric valve
actuators (EVA) may be used to control operation of intake and
exhaust valves, respectively. Each valve may be configured with a
valve position sensor (not shown) that can be used to determine the
position of the valve.
[0014] To reduce the level of NOx emissions, the engine may be
equipped with an EGR system 12. EGR system 12 may comprise a
conduit 32 connecting the exhaust manifold 28 to the intake
manifold 26. This allows a portion of the exhaust gases to be
circulated from the exhaust manifold 28 to the intake manifold 26
in the direction of arrow 31. An EGR valve 34 regulates the amount
of exhaust gas recirculated from the exhaust manifold 28. The valve
34 may be a throttle plate, pintle-orifice, slide valve, or any
other type of variable valve.
[0015] In the combustion chambers, the recirculated exhaust gas
acts as an inert gas, thus lowering the flame and in-cylinder gas
temperature and decreasing the formation of NOx. On the other hand,
the recirculated exhaust gas displaces fresh air and reduces the
air-to-fuel ratio of the in-cylinder mixture by reducing excess
oxygen.
[0016] Turbocharger 14 uses exhaust gas energy to increase the mass
of the air charge delivered to the engine combustion chambers 18.
The exhaust gas flowing in the direction of arrow 30 drives the
turbocharger 14. This larger mass of air can be burned with a
larger quantity of fuel, resulting in more torque and power as
compared to naturally aspirated, non-turbocharged engines.
[0017] The turbocharger 14 includes a compressor 36 and a turbine
38 coupled by a common turbocharger shaft 40. The exhaust gas 30
drives the turbine 38 which drives the compressor 36 which, in
turn, compresses ambient air 42 and directs it (arrow 43) into the
intake manifold 26. The VGT 14 can be modified as a function of
various operating parameters, including engine speed, during engine
operation by varying the turbine flow area and the angle at which
the exhaust gas 30 is directed at the turbine blades. This can be
accomplished by changing the angle of the inlet guide vanes 44 on
the turbine 38. The operating position for the engine guide vanes
44 may be determined from the desired engine operating
characteristics at various engine speeds and loads by ECU 24, or as
described in further detail herein with regard to FIGS. 2-4.
[0018] An aftertreatment device 74 may be disposed downstream of
the turbine 38. Aftertreatment device 74 may include any suitable
type of device for reducing emissions from engine 10. Examples
include, but are not limited to, three-way catalytic converters,
NOx traps, oxidation catalyst, particulate filters, selective
catalytic reduction catalysts, etc. In one example, the
aftertreatment device is a diesel particulate filter. ECU 24 may be
configured to periodically raise the temperature of particulate
filters to regenerate the filters.
[0019] One or more of the engine systems, such as the EGR systems
12 and VGT 14, throttle valves 84, and fuel injectors 20 may be
controlled by a control system including the ECU. For example,
signal 46 from the ECU 24 regulates the EGR valve position, and
signal 48 regulates the position of the VGT guide vanes 44.
[0020] In the ECU 24, the command signals 46, 48 to the EGR system
12 and VGT 14 actuators, as well as other command signals, may be
calculated from measured variables and engine operating parameters.
Sensors and calibratable lookup tables may be used to provide the
ECU 24 with engine operating information. For example, manifold
absolute pressure (MAP) sensor 50 provides a signal 52 to the ECU
24 indicative of the pressure in the intake manifold 26 downstream
of the EGR entrance, and pressure sensor 96 provides a signal 98
indicative of pressure upstream of the EGR entrance in the intake
manifold. Likewise, exhaust manifold pressure (EXMP) sensor 54
provides an EXMP signal 56 to the ECU 24 indicative of the pressure
in the exhaust manifold 28 upstream of the EGR exit. Further, an
air charge temperature sensor 58 provides a signal 60 to the ECU 24
indicative of the temperature of the intake air charge 42. A mass
airflow (MAF) sensor 64 also provides signals 66 indicative of the
airflow in the intake system to the ECU 24.
[0021] In addition, exhaust gas oxygen concentration, which can be
indicative of air-fuel ratio, can be provided by oxygen sensor 72.
Additional sensory inputs can also be received by the ECU along
signal line 62, such as engine coolant temperature, engine speed,
and throttle position. Further, ECU 24 is shown to receive signals
from a gas pedal position from sensor 91 and a brake pedal position
from sensor 93.
[0022] Exhaust gas sensor 72 is shown upstream of an aftertreatment
device 74. Exhaust gas sensor 72 may be any of many known sensors
for providing an indication of exhaust gas air/fuel ratio such as a
linear oxygen sensor, a two-state oxygen sensor, or a hydrocarbon
(HC) or carbon monoxide (CO) sensor. In this particular example,
sensor 38 is a two-state oxygen sensor that provides signal EGO to
controller 12 which converts signal EGO into two-state signal
EGOs.
[0023] Controller 24 may determine the temperature of
aftertreatment device 74 in a variety of ways. For example, the
temperature may be inferred from engine operation. In an alternate
embodiment, temperature may be determined from temperature sensor
81.
[0024] It should be understood that FIG. 1 merely shows one example
multi-cylinder engine, and that each cylinder has its own set of
intake/exhaust valves, fuel injectors, etc.
[0025] It should further be understood that the depicted diesel
engine 10 is shown only as an example, and that the systems and
methods described herein may be implemented in or applied to other
suitable engines having various components and/or arrangement of
components.
[0026] In one embodiment, engine operation is controlled using an
estimate of turbocharger shaft speed. As noted herein, accurate
control of transient rotational speed of the turbocharger may be
used to advantage in systems having high performance turbocharger
operation, as well as for turbocharger protection control
strategies. In this way, turbocharger operation may be controlled
to stay within the manufacturers limits, which are defined by the
use of the relevant flow maps. While the use of look up tables to
limit operation may be useful, the pressure sensors typically used
to measure the pressure produced by the turbocharger in the engine
air intake system may be too indirect and slow to provide an
accurate indication of turbocharger transient performance. On the
other hand, measurement of the turbocharger shaft speed, while
direct, may be difficult due to the harsh ambient and difficult
sealing conditions around the turbocharger. As such, a more
accurate estimate of turbocharger shaft speed can be beneficial,
even if used in addition to direct speed measurement or a
supplement to look-up table based control.
[0027] An accurate determination or estimate of turbocharger shaft
speed may be based on a dynamic observer, thereby eliminating the
need for a sensor, or supplementing sensor information. In one
example, the observer may based on a turbocharger torque balance
(as a dynamic term) and one or more turbocharger maps (as a static
term). Such an approach can include the intake and exhaust side
together with turbine shaft speed. The observer feedback gains may
be determined using an extended Kalman filter, as one example. Such
an observer can provide an estimate of turbocharger shaft speed
with reduced transient delays, while also providing an accurate
match to mapped data in steady state.
[0028] In some cases, accuracy may be further improved by including
an integral term at steady state to compensate for model errors.
For example, such an approach can compensate for complexities in
the turbine and compressor torque calculations.
[0029] Further details of example an example observer is described
below with regard to FIGS. 2-4.
[0030] Referring now to FIG. 2, a routine is described for
controlling engine and turbocharger operation. In 210, the routine
reads various operating conditions, which may include atmospheric
pressure (patm), manifold pressure (MAP), exhaust manifold pressure
(pexh), exhaust temperatures, intake charge temperatures, engine
speed, throttle position, and others. Next, in 212, the routine
determines whether turbocharger operation is enabled. If not, the
routine continues to 220 to set the turbocharger vane position
and/or bypass and/or wastegate valves to a default position, which
may be at a minimum boosting operation position. Otherwise, the
routine continues to 214.
[0031] In 214, the routine determines desired turbocharger
operating parameters based on operating conditions. For example,
the routine may determine a desired boosting level, desired vane
position, desired bypass amount, desired wastegate position,
desired throttle positions, desired airflow and/or others based on
desired engine torque, engine speed, and/or engine load. In one
particular example, the routine may determine desired throttle
positions and vane positions to provide a desired pressure ratio
across the turbine. In another particular example, the routine may
determine desired throttle positions and vane positions to provide
a desired airflow to the cylinders.
[0032] In 216, the routine adjusts one or more determined operating
parameters from 214 based on estimated turbocharger performance
(e.g., based on estimated turbocharger shaft speed) to reduce
transient and/or steady state shaft over-speed operation. Then, in
218, the adjusted parameters are carried out by sending appropriate
control signals from the control system to the actuators. Further,
the routine may adjust other engine operating parameters to
counteract any torque reduction caused by the speed limiting
operation. For example, fuel injection amount and/or timing may be
temporarily increased during adjustment due to over-speed
operation.
[0033] In one embodiment, an estimated shaft speed is used as
described with regard to FIG. 3 to adjust vane position to reduce
boosting if the estimated shaft speed exceeds a limit value, where
the limit value may vary with operating conditions such as
temperature. For example, the routine may adjust the vane position
to reduce shaft speed. In another example, the routine may
temporarily increase wastegate opening to reduce a transient shaft
over-speed condition. In still another example, the routine may
temporarily increase a bypass around the compressor to reduce a
transient shaft over-speed condition. In still another example, the
routine may temporarily reduce intake airflow (e.g., by closing an
intake manifold throttle and/or by adjusting valve operation of a
variable cylinder valve timing and/or lift system) to reduce shaft
speed. Further, combinations of adjustments maybe used, such as
those just noted.
[0034] Referring now to FIG. 3, a routine is described for
dynamically determining turbocharger shaft speed based at least on
intake and exhaust manifold conditions using a torque balance
across the turbocharger. As noted above, an observer based on a
torque balance across the turbocharger may be used along with an
additional integral feedback term.
[0035] Specifically, in 310, the routine determines an estimated
steady state shaft speed via look-up tables and turbocharger
mapping information. In one example, the steady state speed ({tilde
over (.omega.)}) can be determined based on a functions (e.g.,
manufacturer compressor tables) of pressure ratio of the compressor
and the mass airflow in the compressor (e.g., MAF) at the current
condition. For example, the following equation may be used:
{tilde over (.omega.)}=f(pr_comp,maf_red)
[0036] Next, in 312, the routine determines whether a change in the
determined steady state speed compared to a previous value is
greater than a threshold amount. If so, the routine continues to
314 to freeze the integrator in the observer. In particular, the
integral term may add over and/or undershoot when settling into
steady state. However, as the integral term is used primarily in
steady state, it can be turned off or reduced during transient
conditions via 312. Otherwise, the routine continues to 314 to
interrogate the observed to update the dynamic shaft speed estimate
as indicated below. In one particular example, the observer may
lead to turbocharger shaft speed by using energy conservation
law:
J tc .omega. t = M t - M c ##EQU00001## M c = m . c .omega. .eta. c
, is c pi T i n [ c k i - 1 k i - 1 ] ##EQU00001.2## M t = 1
.omega. m . t c pe .eta. t , is T em [ 1 - t 1 - k e k e ]
##EQU00001.3##
Where,
[0037] .omega.--turbocharger shaft speed J.sub..omega.--inertia of
the turbocharger shaft T.sub.in--temperature of compressor inlet
air T.sub.em--temperature of tubine inlet gas {dot over
(m)}.sub.c--compressor air mass flow rate {dot over
(m)}.sub.t--turbine gas mass flow rate C.sub.pa--specific heat of
air C.sub.pe--specific heat of exhaust gas
.eta..sub.c,is--adiabatic efficiency of the compressor
.eta..sub.t,is--adiabatic efficiency of the turbine
.PI..sub.c--pressure ratio of the compressor .PI..sub.t--pressure
ratio of the turbine The observer may then be designed as:
.omega. t = 1 J tc ( M t - M c ) + K p ( .omega. ~ - .omega. ) + K
i .intg. ( .omega. ~ - .omega. ) t ##EQU00002##
Calculation of turbocharger shaft speed in the discrete time
domain:
.omega. n - 1 = .omega. n + ( M t n - M c n ) .DELTA. t J tc + K p
.DELTA. t ( .omega. n - .omega. ~ n ) + K i .DELTA. t [ x n ]
##EQU00003##
where
{tilde over (.omega.)}.sup.n=look_up(pr_comp,maf_red)
x.sup.n=x.sup.n-1+({tilde over
(.omega.)}.sup.n-1-.omega..sup.n-1).DELTA.t
Further, .DELTA.t is the time step between the update of the
observer calculation. In this way, it is possible to estimate
transient turbocharger shaft speed, and when this dynamic estimate
exceeds a value, actions can be taken to temporarily limit the
speed, such as opening the a vane position or bypass valve. This
can improve turbocharger over-speed compensation at altitude, thus
enabling more aggressive turbocharger operation at both sea level
and altitude. Further, this can enhance turbocharger life by
reducing transient over-speed conditions. Further, still, this can
lead to better robustness to modeling errors because of a closed
loop observer design and steady state stabilization.
[0038] Referring now to FIG. 4, example data is shown using the
above described observer. Specifically, FIG. 4 shows a prophetic
simulation showing simulated actual shaft speed (solid line,
spd_mes), the observer estimate (long dash, long dash,
spd_est_obs), and the steady state speed value (long dash, short
dash, spd_est_lkp). In this example, the observer uses measured
mass flow, pressures and temperature. The data shows close tracking
of turbocharger shaft speed and suppression of intake manifold
pressure phase delay. Further, it also highlights the compensation
of transient behavior not followed by the static turbo performance
map.
[0039] In addition to monitoring and reducing turbocharger shaft
over-speed conditions, the estimate may also be used for
model-based diagnosis, such as monitoring vane position, wastegate
conditions, etc.
[0040] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various acts, operations, or functions
illustrated may be performed in the sequence illustrated, in
parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated acts or functions may be repeatedly performed
depending on the particular strategy being used. Further, the
described acts may graphically represent code to be programmed into
the computer readable storage medium in the engine control
system.
[0041] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and nonobvious combinations and subcombinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0042] The following claims particularly point out certain
combinations and subcombinations regarded as novel and nonobvious.
These claims may refer to "an" element or "a first" element or the
equivalent thereof. Such claims should be understood to include
incorporation of one or more such elements, neither requiring nor
excluding two or more such elements. Other combinations and
subcombinations of the disclosed features, functions, elements,
and/or properties may be claimed through amendment of the present
claims or through presentation of new claims in this or a related
application. Such claims, whether broader, narrower, equal, or
different in scope to the original claims, also are regarded as
included within the subject matter of the present disclosure.
* * * * *